1. Field
The disclosed embodiments belong to the field of hydraulic systems used on board aircraft for controlling moving elements such as aerodynamic control surfaces and portions of the landing gear. More particularly, the disclosed embodiments relate to a hydraulic system protected against the consequences of the breakage of certain lines due to an external impact.
2. Brief Description of Related Developments
On most modern transport aircraft, numerous moving parts are moved by actuators using power transported in a pressurized hydraulic fluid.
The aerodynamic control surfaces are the main systems moved by hydraulic actuators, their satisfactory operation and their fluid supplies by hydraulic distribution systems are essential, and any uncontrolled failure is liable to imperil the aircraft.
For these safety reasons, the hydraulic systems of an aircraft, comprising hydraulic power generation systems, hydraulic distribution systems and actuators, are arranged in architectures which attempt, inter alia, to limit the consequences of potential failures of the various components of said systems and, in all cases, to prevent a probable failure from having consequences that are liable to jeopardize the integrity of the aircraft concerned.
Principles common to all known architectures, at least for those used on board civilian aircraft required to meet stringent certification standards, consist in arranging a plurality of independent hydraulic circuits, in general three circuits, each circuit possibly comprising two or more of certain components, for example two pumps for generating hydraulic pressure (redundancy rules), and furthermore, in arranging the components of said circuits on board the aircraft so that the risk of damage to two or more redundant circuits or components, due to a single damaging event, is improbable (segregation rule).
However, in the case of an external event, such as midair collision or missile impact on one of the two wings of the aircraft airfoil, the risk is high of simultaneously cutting lines of all the hydraulic circuits having lines on said wing, and the hydraulic circuits affected by the event rapidly lose hydraulic fluid and become unusable. In this case, since the hydraulic pressure is no longer distributed to the systems which participate in controlling the aircraft in flight, flight control of the aircraft is considered impossible.
To contend with the loss of all the hydraulic fluid of the hydraulic circuits in case of breakage of a line during a midair collision affecting a wing tip or stabilizer root, one solution consists in inserting hydraulic fuses in the lines to said wing tips or to the stabilizer root.
However, this solution is not satisfactory because the locations of said hydraulic fuses are unsuitable for isolating the hydraulic circuit or circuits from the damage caused by the impact of a missile or any destructive device on one of the aircraft wings, between the root of said wing at the fuselage and the wing tip.
An appropriate system for protecting the hydraulic circuits in the wings of the airfoil is necessary in order to preserve the capacity to control the aircraft by the protected hydraulic systems.
The disclosed embodiments describe a hydraulic system which comprises at least one hydraulic circuit, said hydraulic circuit comprising:
at least one hydraulic pump for generating a high pressure flow of a hydraulic fluid of the at least one hydraulic circuit, said pump defining a direction upstream of the hydraulic circuit,
one or more consumer equipment units of a first zone using the hydraulic fluid, said consumer equipment units defining a direction downstream of the hydraulic circuit,
at least one HP discharge line in which the hydraulic fluid flows from the pump to the consumer equipment units, said HP discharge line comprising at least one bypass to consumer equipment units of a second zone, in which second zone the hydraulic pump is located, said bypass being located between, on the one hand, the pump and, on the other hand, the consumer equipment units,
at least one return line in which the hydraulic fluid flows from the consumer equipment units to a hydraulic tank, said return line comprising at least one bypass to consumer equipment units of a second zone, said bypass being located between, on the one hand, the tank and, on the other hand, the consumer equipment units.
According to the disclosed embodiments, the hydraulic system further comprises:
at least one closure element, on the at least one HP discharge line of the at least one hydraulic circuit between, on the one hand, the bypass and, on the other hand, the consumer equipment units,
at least one nonreturn valve on the at least one return line of the at least one hydraulic circuit between, on the one hand, the bypass and, on the other hand, the consumer equipment units, and opposing the flow of the fluid from the pump to the consumer equipment units.
Said at least one closure element comprises an open position in which the hydraulic fluid flows freely in the HP discharge line from upstream to downstream of the closure element in a normal operating mode of the hydraulic circuit and comprises a closed position in which the hydraulic fluid is prevented from flowing from upstream to downstream of the closure element, the closure element being placed automatically in the closed position when a break of the HP discharge line is detected downstream of the closure element of said HP discharge line.
In a first embodiment, the at least one closure element is at least one fuse which is normally open and which closes, without external action, when a flow rate of fluid passing through the line at said fuse is higher than a predefined threshold flow rate, characteristic of the rating of the fuse concerned.
When the hydraulic system comprises at least two fuses on a HP discharge line, the second fuse is downstream of the first.
The distance between two consecutive fuses on a HP discharge line is determined so that:
the rating of the fuse is at least higher than the maximum normal operating flow rate of all the consumer equipment units located downstream of the fuse,
the rating of the fuse is lower than the flow rate in case of breakage of the HP discharge line downstream of the fuse and upstream of the next downstream fuse.
The number of fuses required and their arrangements are determined, for a given temperature of the hydraulic fluid, to detect a breakage at any point of the HP discharge line.
For example, the first zone comprising one or more consumer equipment units is an aircraft wing.
In another embodiment, the at least one closure element is a controlled valve.
The valve is controlled when a signal from at least one pressure sensor detects a pressure lower than a predefined threshold in a HP discharge line at a point close to a consumer equipment unit among the furthest from the controlled valve.
Preferably, the at least one sensor is positioned on a HP discharge line close to one tip of an aircraft wing.
The disclosed embodiments also relate to an aircraft comprising at least two hydraulic circuits, each circuit supplying consumer equipment units which are specific to it and in which at least one circuit, comprises lines in the two wings of said aircraft.